THERMO Spoken Here! ~ J. Pohl © ~ 2017 (B2000-085)

Manometer and Bourdon Gage

The elevation of the horizontal pipe is slightly above sea level. Water flows through a pipe that has been fitted with a manometer and a Bourdon gage. Use the readings of the manometer and Bourdon gage:

Calculate the pressure of water flowing through the pipe.
♦   We always start at a place in space where the pressure of the fluid is known.

Manometer  At the center-line of the pipe but outside in the air about it; the pressure there is atmospheric pressure. Let that point be our first (known) pressure. The path now moves upward 142mm to the upper surface of the mercury. From there follow a hydrostatic path through the mercury (gage) to the center-line of the flow of water.

patm + 13,600 kg/m39.81 m/s2(0.284 m) -1,000 kg/m³9.81 m/s2(0.142 m) = 137.8 kPa

Bourdon Gage:  This gage is connected to the side of the pipe at its center-line. Thus atmospheric pressure plus the gage reading (G.R.) will equal the pressure of the water inside the pipe.

patm + G.R. = pwater   or         101.3 kPa + 38 kPa = 139 kPa

One pascal of pressure difference is very small. The Bourdon gage might be incorrect - it had to be calibrated. The water pressure should decrease in the direction of flow.

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